Winding of coils for transformers is a well known art and many different transformer configurations have been used in the past and are available today. Typically, a transformer coil includes a bobbin having a number of layers of wound wire, each layer of wound wire applied over a prior layer of wound wire.
In the manufacture of coils, it sometimes becomes necessary to tap a lead from an intermediate layer of wound wire, i.e., a layer wound about the bobbin, onto which an additional layer or layers are to be wound. The previously available process for tapping such a lead from the coil during manufacture is rather cumbersome. For example, if a tap is to be made at a point midway across a layer of wound wire, the winding process must be halted in order that a certain amount of wire can be unwound from the wire feed spool and from the transformer coil bobbin itself. The two wire ends are then secured by twisting and anchoring them outside of the winding area of the coil bobbin.
The winding process is then resumed at the point on the layer where the tap was made. The winding for that layer proceeds until the end of the layer is reached. Winding then stops again, so that spacers may be attached to the bobbin in such a manner that the difference in height between the pre-tap portion of the wound coil and the post-tap portion can be eliminated. The subsequent layer is then wound over the tapped layer and the spacers. The winding process at this stage is slow and often results in a misalignment of layers on wound over the tapped layer. In the situation where a precision winding pattern is required, the tapping process described above often adversely effects the precision of the pattern, resulting in a high reject rate. As used herein, the term "precision winding" means that the wire in each layer makes the same number of turns, and the turns of successive layers are not randomly placed but are neatly stacked or nested one on top of another. Each turn of wire is wound immediately adjacent the wire of the previous turn, in a generally spiral pattern about the bobbin core or other winding axis. The winding pattern is not strictly spiral. Rather, the wire is would normal to the winding axis about most of the winding axis; the wire advances to the next position at a crossover point. In the case of a rectangular bobbin, the wire is wound normal to the axis for three of the four sides of the bobbin. Between the third and fourth corners of the rectangle the wire is angled to rest adjacent the wire from the previous turn at corner 4. This pattern is repeated throughout the winding of the layer, such that the turns are parallel to one another for three of the four sides of the bobbin; the crossover point is consistently on one side of the bobbin.